Water and wastewater treatment system and process for contaminant removal

Abstract

A system and process for removing contaminants from water and wastewater, where the water or wastewater is transformed into purified water that can be discharged to the environment. Wastewater is transported through several stations for purification, including an electrochemical cell. The purification process begins by sending the wastewater to a classifier through an in-line basket strainer. The wastewater stream in the classifier is drawn through a solid-liquid hydrocyclone, which returns the solids to the classifier and sends the remaining liquid to feed tanks. Contaminants that float are removed from the wastewater by skimming from the surface of the feed tank. The wastewater underflow from the feed tanks is pumped directly to the electrochemical cell where it enters into the bottom of the cell, and exits from the top of the cell. The discharge, including coagulated solids, hydrogen gas, and oxygen gas, is mixed with a polymer as well as compressed air just prior to entering a static in-line mixer. The resulting mixture flows past a vertical vent pipe to a flotation cell. The underflow of the flotation cell, which is substantially free of coagulated solids, flows by gravity to a settling tank where any remaining solids sink to the bottom. The solid-free liquid (water) exits the settling tank over an overflow weir and is pumped through a plurality of bag filters and finally through a polymeric filter to remove remaining contaminants.

We claim:  
     
       1. A process for removing contaminants from a wastewater stream, comprising: 
       (a) feeding the wastewater stream into an electrochemical cell comprising at least a pair of conductive plates stacked in parallel spaced relation, wherein electricity is passed into said conductive plates and through the wastewater stream to produce a coagulated stream;  
       (b) injecting a coagulating reagent into the coagulated stream from the electrochemical cell and passing the coagulated stream to a mixer, wherein said mixer contacts precipitated solids present in the coagulated stream with said coagulating reagent to produce a reagent-mixed liquid;  
       (c) passing the reagent-mixed liquid from said mixer past a vent and into a flotation cell where a flotation cell liquid is produced through the removal of a majority of coagulated particles from the reagent-mixed liquid.  
     
     
       2. The contaminant removal process of  claim 1 , further comprising a step of injecting compressed air into the coagulated stream from the electrochemical cell prior to passing the coagulated stream to the mixer. 
     
     
       3. The contaminant removal process of  claim 2 , further comprising a step of injecting compressed air into the wastewater stream before the wastewater stream is passed to said electrochemical cell. 
     
     
       4. The contaminant removal process of  claim 2 , wherein the flotation cell liquid is produced when coagulated particles rise to the surface due to buoyancy caused by the compressed air associated with the particles and are separated from the liquid at the surface. 
     
     
       5. The contaminant removal process of  claim 1 , further comprising a step of injecting compressed air into the wastewater stream before the wastewater stream is passed to said electrochemical cell. 
     
     
       6. The contaminant removal process of  claim 1 , further comprising a step of feeding the wastewater stream to a classifier prior to passing the wastewater stream to said electrochemical cell, wherein a classifier stream is produced by settling out larger particles from the wastewater stream to the bottom of the classifier. 
     
     
       7. The contaminant removal process of  claim 6 , further comprising a step of removing solids from said classifier. 
     
     
       8. The contaminant removal process of  claim 7 , wherein an auger is used to remove the solids from a bottom region of said classifier. 
     
     
       9. The contaminant removal process of  claim 6 , further comprising a step of passing the classifier stream to a solid/liquid hydrocyclone, wherein the heavier components of the wastewater stream are returned back to said classifier and the remaining wastewater stream is passed on to the electrochemical cell. 
     
     
       10. The contaminant removal process of  claim 6 , further comprising a step of passing the classifier stream to a feed tank, wherein a feed tank stream is produced. 
     
     
       11. The contaminant removal process of  claim 10 , wherein the feed tank stream has an oily component. 
     
     
       12. The contaminant removal process of  claim 11 , further comprising a step of skimming free oil from a top surface of the feed tank stream. 
     
     
       13. The contaminant removal process of  claim 12 , further comprising a step of sending the free oil to a storage tank and of decanting the free oil from said storage tank. 
     
     
       14. The contaminant removal process of  claim 12 , further comprising a step of passing liquid present underneath the free oil in said storage tank back to said classifier. 
     
     
       15. The contaminant removal process of  claim 1 , further comprising a step of removing large particulates from the wastewater stream prior to passing the wastewater stream to said electrochemical cell. 
     
     
       16. The contaminant removal process of  claim 15 , wherein the large particles are removed from the wastewater stream by a strainer. 
     
     
       17. The contaminant removal process of  claim 1 , further comprising a step of adding a second coagulating reagent to the wastewater stream before the wastewater stream is passed to said electrochemical cell. 
     
     
       18. The contaminant removal process of  claim 17 , wherein the second coagulating reagent is a polymer. 
     
     
       19. The contaminant removal process of  claim 1 , wherein said conductive plates are oriented horizontally. 
     
     
       20. The contaminant removal process of  claim 1 , further comprising a step of periodically reversing the polarity of said conductive plates. 
     
     
       21. The contaminant removal process of  claim 1 , wherein said conductive plates are aluminum or iron. 
     
     
       22. The contaminant removal process of  claim 1 , wherein each successive plate is sealed to an opposite end of a housing of said electrochemical cell and to both opposing side walls of said housing, creating a serpentine path for the wastewater stream to travel from an inlet at a bottom of said electrochemical cell to an outlet in a top of said electrochemical cell, wherein said electrochemical cell also includes a first and second electrical headers, wherein each of said conductive plates is in electrical communication with either said first or said second header. 
     
     
       23. The contaminant removal process of  claim 22 , wherein said conductive plates are aluminum or iron where the product of electrical current in amperes and the hydraulic residence time in minutes per electroplate surface area in square meters is greater than 20 amp minutes/square meter. 
     
     
       24. The contaminant removal process of  claim 22 , wherein a side cover of said housing is removable, allowing said conductive plates to be changed. 
     
     
       25. The contaminant removal process of  claim 1 , further comprising a step of re-circulating a portion of the coagulated stream through said electrochemical cell. 
     
     
       26. The contaminant removal process of  claim 25 , wherein the flow rate of said portion of the coagulated stream that is re-circulated to the electrochemical cell is sufficient to cause turbulent mixing of the wastewater with the metal ions released from the plates and sufficient to cause scouring of the plates. 
     
     
       27. The contaminant removal process of  claim 1 , wherein said coagulating reagent is a polymer. 
     
     
       28. The contaminant removal process of  claim 1 , wherein said coagulated particles present in said reagent-mixed liquid flow over an overflow weir into a solids collection tank. 
     
     
       29. The contaminant removal process of  claim 28 , further comprising a step of passing solids from said solids collection tank and said settling tank to a filter press, wherein liquid is removed from the solids and is sent to said classifier. 
     
     
       30. The contaminant removal process of  claim 1 , further comprising a step of passing the flotation cell liquid from said flotation cell to a settling tank where a substantially solid-free liquid is produced. 
     
     
       31. The contaminant removal process of  claim 30 , further comprising a step of passing the substantially solid-free liquid from the settling tank through at least one filter. 
     
     
       32. The contaminant removal process of  claim 31 , wherein said at least one filter includes one or both of a bag filter and a polymeric filter. 
     
     
       33. The contaminant removal process of  claim 1 , wherein the mixer is a static mixer. 
     
     
       34. The contaminant removal process of  claim 33 , wherein the static mixer is an in-line mixer. 
     
     
       35. A process for removing contaminants from a wastewater stream including an oily component, comprising: 
       (a) feeding the wastewater stream into a classifier;  
       (b) passing the wastewater stream from the classifier to a plurality of feed tanks where a feed tank stream is produced;  
       (c) skimming free oil from a top surface of the feed tank stream in said feed tanks and sending the free oil to a storage tank;  
       (d) decanting the free oil from said storage tank;  
       (e) passing liquid present underneath the free oil in said storage tank back to said classifier;  
       (f) passing the feed tank stream from said feed tanks to an electrochemical cell, having conductive plates stacked in parallel spaced relation such that each successive plate is sealed to an opposite end of a housing of said electrochemical cell and to both opposing side walls of said housing, creating a serpentine path for the feed tank stream to travel from an inlet at a bottom of said electrochemical cell to an outlet in a top of said electrochemical cell, wherein said electrochemical cell also includes a first and second electrical header, wherein each successive conductive plate is in electrical communication with either said first or said second header alternatingly, wherein electricity is passed into said conductive plates and through the feed tank stream to produce a coagulated stream;  
       (g) re-circulating a portion of the coagulated stream through said electrochemical cell, at a sufficient flow rate to cause turbulent mixing of the wastewater and the metal was released from the plates and to cause scouring of the plates;  
       (h) injecting compressed air and a coagulating reagent into the coagulated stream from the electrochemical cell and passing the coagulated stream to an in-line mixer, wherein said in-line mixer contacts precipitated solids present in the coagulated stream with said coagulating reagent to produce a reagent-mixed liquid;  
       (i) passing the reagent-mixed liquid from said in-line mixer past a venting apparatus and into a flotation cell where a flotation cell liquid is produced through the removal of a majority of coagulated particles from the reagent-mixed liquid, wherein said coagulated particles present in said reagent-mixed liquid flow over an overflow weir into a solids collection tank;  
       (j) passing the flotation cell liquid from said flotation cell to a settling tank where a substantially solid-free liquid is produced;  
       (k) passing solids from said solids collection tank and said settling tank to a filter press, wherein liquid is removed from the solids and is sent to said classifier; and  
       (l) passing the substantially solid-free liquid from said settling tank through at least one filter to obtain a final discharge.  
     
     
       36. The contaminant removal process of  claim 35 , further comprising a step of removing large particulates from the wastewater stream prior to passing the wastewater stream to the classifier. 
     
     
       37. The contaminant removal process of  claim 36 , wherein the large particles are removed from the wastewater stream by an in-line basket strainer. 
     
     
       38. The contaminant removal process of  claim 35 , further comprising a step of removing solids from a bottom of said classifier. 
     
     
       39. The contaminant removal process of  claim 38 , wherein an auger is used to remove the solids from a bottom of said classifier. 
     
     
       40. The contaminant removal process of  claim 35 , further comprising a step of passing the wastewater stream from the classifier to a solid/liquid hydrocyclone, wherein the heavier components of the wastewater stream are returned back to said classifier and an oily liquid stream is passed to said feed tanks. 
     
     
       41. The contaminant removal process of  claim 35 , further comprising a step of injecting compressed air into the feed tank stream before it is passed to said electrochemical cell. 
     
     
       42. The contaminant removal process of  claim 35 , further comprising a step of adding a second coagulating reagent to the feed tank stream before the feed tank stream is passed to said electrochemical cell. 
     
     
       43. The contaminant removal process of  claim 42 , wherein the second coagulating reagent is a polymer. 
     
     
       44. The contaminant removal process of  claim 35 , wherein said conductive plates are oriented horizontally. 
     
     
       45. The contaminant removal process of  claim 35 , further comprising a step of periodically reversing the polarity of said conductive plates. 
     
     
       46. The contaminant removal process of  claim 35 , wherein said conductive plates are aluminum. 
     
     
       47. The contaminant removal process of  claim 46 , wherein the product of electrical current in amperes and the hydraulic residence time in minutes per electroplate surface area in square meters is greater than 20 amp minutes/square meter. 
     
     
       48. The contaminant removal process of  claim 35 , wherein a side cover of said housing is removable, allowing said conductive plates to be changed. 
     
     
       49. The contaminant removal process of  claim 35 , wherein the flow rate of said portion of the coagulated stream that is re-circulated to the electrochemical cell is sufficient to provide turbulent mixing and scouring of the conductive plates. 
     
     
       50. The contaminant removal process of  claim 35 , wherein said coagulating reagent is a polymer. 
     
     
       51. The contaminant removal process of  claim 35 , wherein said at least one filter includes one or both of a bag filter and a polymeric filter. 
     
     
       52. A wastewater treatment apparatus for a wastewater treatment system having an electrochemical cell for electrocoagulation of the wastewater, a flotation tank downstream of the cell for flotation separation of solids from the wastewater and a conduit connecting the cell to the flotation tank to direct wastewater from the cell to the tank, the treatment apparatus comprising: 
       (a) a reagent dispenser communicating with the conduit to dispense a coagulation-inducing reagent into the wastewater in the conduit; and  
       (b) a mixer communicating with the wastewater in the conduit downstream from the point where the reagent is dispensed into the conduit, the mixer mixing the wastewater in the conduit with the reagent to cause coagulation of the solids in the wastewater and with gas in the wastewater to cause at least some of the solids in the wastewater to be directed upwardly to the surface due to the buoyancy force of the gas acting on the solids when the wastewater is in the flotation tank after discharge from the conduit.  
     
     
       53. The apparatus of  claim 52 , further comprising a compressed gas dispenser communicating with the conduit to dispense compressed gas into the wastewater in the conduit upstream of the mixer. 
     
     
       54. The apparatus of  claim 52 , wherein the reagent dispensed by the reagent dispenser is a coagulation-inducing polymer. 
     
     
       55. The apparatus of  claim 52 , wherein the mixer is housed within the conduit. 
     
     
       56. The apparatus of  claim 55 , wherein the mixer is an in-line static mixer. 
     
     
       57. The apparatus of  claim 52 , further comprising a vent positioned downstream of the mixer and communicating with the conduit to remove at least some of the gas from the conduit. 
     
     
       58. The apparatus of  claim 52 , wherein the compressed gas is air. 
     
     
       59. A wastewater treatment system for removing contaminants from wastewater, comprising: 
       (a) an electrochemical cell for electrocoagulation of contaminants in the wastewater, the cell comprising an inlet for directing wastewater into the cell and an outlet for directing wastewater from the cell and a pair of oppositely charged spaced conductive plates for directing the wastewater between the plates and for electrocoagulation of solids in the wastewater when electricity is passed into the plates;  
       (b) a flotation tank for flotation separation of solids from the wastewater;  
       (c) a first conduit connecting the outlet of the electrochemical cell with the flotation tank;  
       (d) a reagent dispenser for dispensing a coagulation-inducing reagent into the wastewater in the conduit;  
       (e) a compressed gas dispenser for dispensing compressed gas into the wastewater in the conduit; and  
       (f) a mixer communicating with the wastewater in the conduit downstream from the point where the reagent and the compressed gas are dispensed into the conduit, the mixer mixing the wastewater in the conduit, travelling from the electrochemical cell, with the reagent to cause coagulation of solids in the wastewater, and with the compressed gas to cause at least some of the solids in the wastewater to be directed upwardly to the surface due to the buoyancy force of the gas acting on the solids when the wastewater is in the flotation tank after discharge from the conduit.  
     
     
       60. The system of  claim 59 , wherein the electrochemical cell comprises: 
       (a) a housing comprising a pair of opposed side walls and end walls connected together;  
       (b) a plurality of conductive plates stacked in parallel spaced relation such that each successive plate is sealed to an opposite end wall of the housing and to both opposing side walls of the housing, creating a serpentine path for the wastewater stream to travel from the inlet to the outlet past the plates; and  
       (c) first and second electrical headers with each successive conductive plate in electrical communication with either the first or the second header alternatingly.  
     
     
       61. The system of  claim 60 , wherein the conductive plates are oriented horizontally. 
     
     
       62. The system of  claim 60 , wherein a side cover or end wall of said housing is removable, allowing said conductive plates to be changed. 
     
     
       63. The system of  claim 59 , further comprising a feed tank for storing wastewater prior to entering the cell, the feed tank connected to the inlet to direct wastewater from the feed tank to the cell. 
     
     
       64. The system of  claim 63 , further comprising an oil skimmer communicating with the feed tanks for skimming free oil from the surface of the wastewater in the feed tank. 
     
     
       65. The system of  claim 64 , further comprising a hydrocyclone for separating heavier components of the wastewater from lighter components of the wastewater, the hydrocyclone connected to the inlet such that the lighter components of the wastewater from the hydrocyclone are directed into the inlet. 
     
     
       66. The system of  claim 65 , further comprising a classifier for gravity settling of heavier components of the wastewater, the classifier connected to the hydrocyclone such that the heavier components of the wastewater from the hydrocyclone are directed to the classifier. 
     
     
       67. The system as described in  claim 66 , further comprising a strainer for removing large particulates from the wastewater prior to the wastewater entering the classifier. 
     
     
       68. The system of  claim 66 , wherein the classifier comprises an auger for removing solids settled from the wastewater in the classifier. 
     
     
       69. The system of  claim 63 , further comprising a hydrocyclone for separating heavier components of the wastewater from lighter components of the wastewater, the hydrocyclone connected to the feed tank such that the lighter components of the wastewater from the hydrocyclone are directed into the feed tank. 
     
     
       70. The system of  claim 69 , further comprising a conduit connected to the feed tank at one end and the hydrocyclone at the other end for directing flow of the lighter components of the wastewater from the hydrocyclone to the feed tank. 
     
     
       71. The system of  claim 59 , further comprising a strainer connected to the inlet for removing large particulates from the wastewater prior to the wastewater entering the inlet. 
     
     
       72. The system of  claim 59 , further comprising a vent positioned downstream of the mixer and communicating with the first conduit to remove at least some of the gas from the first conduit. 
     
     
       73. A The system of  claim 59 , further comprising a re-circulation conduit connected to the first conduit at one end and to the inlet at the other end, for directing a portion of the wastewater from the first conduit back to the inlet to be reintroduced into the cell. 
     
     
       74. The system of  claim 73 , further comprising a flow adjuster for adjusting the volume of wastewater flowing through the re-circulation conduit. 
     
     
       75. The system of  claim 59 , wherein the flotation tank comprises an overflow weir removing liquid and coagulated solids from the surface of the wastewater in the flotation tank. 
     
     
       76. The system of  claim 75 , further comprising a solids collection tank for collecting the coagulated solids and liquid from the overflow weir. 
     
     
       77. The system of  claim 76 , further comprising a filter press communicating with the solids collection tank to receive the coagulated solids and liquid in the solids collection tank and to filter the coagulated solids from the liquid. 
     
     
       78. The system of  claim 77 , further comprising a return conduit connected to the filter press at one end and the classifier at the other end for directing the liquid component of the coagulated solids and liquid passing through the filter press back to the classifier. 
     
     
       79. The system of  claim 77 , further comprising a settling tank connected to the flotation tank to receive the remaining wastewater following removal of the coagulated solids by the weir, the settling tank permitting the settling of particles in the remaining wastewater by gravity to the bottom of the settling tank. 
     
     
       80. The system of  claim 79 , further comprising a settling tank conduit connected to a bottom region of the settling tank at one end and to the filter press at the other end for directing solids and liquids in the bottom region of the settling tank to the filter press. 
     
     
       81. The system of  claim 80 , further comprising a filter connected to the settling tank to receive the wastewater in the settling tank remaining after removal of the solids and liquid from the bottom of the settling tank to remove substantially all the remaining particles from the wastewater leaving a final discharge of liquid flowing from the filter.